1. Field of the Invention
The present invention relates to a refrigerant distribution device and method for use in a refrigeration system having a compressor, condenser, expansion device, and an evaporator.
2. Background Art
In a typical air conditioning system, high-pressure liquid refrigerant from a condenser enters an expansion device where pressure is reduced. The refrigerant at the exit of the expansion device consists of a mixture of low-pressure refrigerant liquid and vapor. This mixture enters an evaporator where more of the liquid becomes vapor while the refrigerant absorbs energy from the heat exchanger as it cools the air to the conditioned space. In evaporator heat exchangers that are constructed of multiple parallel heat transfer tubes, the incoming refrigerant liquid-vapor mixture typically enters a common manifold that feeds multiple tubes simultaneously.
Due to gravity and momentum effects, the liquid refrigerant separates from the vapor refrigerant and stays at the bottom of the tube. The liquid refrigerant will proceed to the end of the manifold and feed more liquid refrigerant into the tubes at the manifold end than the tubes adjacent the inlet tube to the manifold. This results in uneven feeding of refrigerant into the heat transfer tubes of the heat exchanger, causing less than optimal utilization of the evaporator heat exchanger.
As the liquid refrigerant absorbs heat it boils or evaporates. If some tubes have less liquid refrigerant flowing through them to boil, some parts of the heat exchanger may be under utilized if all of the liquid refrigerant boils well before the exit of the heat transfer tubes.
As the refrigerant evaporator delivers cold air, it is desirable that the temperature distribution in the emergent air flow be relatively uniform. This goal is complicated by the fact that numerous refrigerant passages may deliver non-uniform cold air.
It is known that other things being equal, a vapor phase flows in a refrigerant passage along the upper space in a horizontally oriented refrigerant distribution pipe. The liquid phase typically flows in a refrigerant passage along the lower volume of the refrigerant distribution pipe. In this way, refrigerant flow conventionally is separated. This phenomenon has complicated the task of distributing refrigerant fluid uniformly inside and along the several refrigerant passages of a refrigerant distribution system.
Another complicating factor is that the more remote the refrigerant is from an inlet side of a system including several refrigerant evaporation passages, the more difficult it is for the liquid refrigerant to flow uniformly. Conversely, the closer the refrigerant is to the inlet side, the more difficult it is for the liquid refrigerant to flow. As a result, the cooling characteristics of air passing around the refrigerant evaporation passage proximate the inlet side and that passing around distal refrigerant evaporation passages is unequal. Consequently, temperature of air passing around the refrigerant evaporation passage at the inlet side differs from that surrounding the distal refrigerant evaporation passages. This phenomenon tends to cause an uneven distribution of temperature in the emergent cold air.
A prior art search revealed the following references: U.S. Pat. No. 6,449,979; U.S. Pat. No. 5,651,268; U.S. Pat. No. 5,448,899; GB 2 366 359, the disclosures of which are incorporated here by reference.
The '979 patent mostly deals with refrigerant distribution in automotive evaporators. The idea is to control the refrigerant flow down the manifold by employing a series of progressively smaller holes. See, e.g., FIGS. 1 & 2.
The '268 patent discloses an apparatus for improving refrigerant distribution in automotive evaporators. The fundamental concept is to mix the refrigerant liquid and vapor at the evaporator inlet and control the distribution of the tubes through small holes that are located around the inlet tube. See, e.g., FIGS. 9 & 12.
The '899 patent discloses a system which separates the liquid refrigerant from the vapor at the evaporator inlet through gravity. Vapor is channeled to the evaporator outlet and only liquid refrigerant is allowed to proceed through the heat exchanger. One limitation of this approach is that the heat exchanger orientations be such that gravity separates the liquid and vapor. Additionally, this approach is most suitable for plate-type evaporators and may not function effectively in other types of evaporators.
GB 2 366 359 teaches an arrangement of four heat exchanger sections which controls refrigerant flow such that it balances the refrigerant heat transfer. However, there is a non-uniform refrigerant distribution in each section which impedes efficient utilization of the heat exchanger.